Method of manufacturing sulfuric acid.



ANDREW MILLER FAIRLIE, F COIPPEBHILL, TENNESSEE.

METHOD OF MANUFACTURING SULFURIC ACID.

No Drawing.

To all 'tv/wm it may concern.-

Be it known that I, ANDREW MILLER FAIRLIE, a citizen of the United States, re-

siding at Copperhill, in the county of Folk and State of lennessee, have invented certain new and useful Improvements in Methods of Manufacturing Sulfuric Acid, of

which the following'is a specification.

My invention relates to processes for the manufacture of sulfuric acid which use some. compound of nitrogen (for example nitrogen oxids, nitrate of soda, or nitric acid,- hereinafter referred to as. nitrogen-oxygen compound) as a means for causing the oxidation of sulfur dioxid in the presence of moisture. As an example of such processes, the method of manufacture known as the chamber process may be cited.

Broadly speaking, the object of my invention is to so control the process that precisely that proportion of. nitrogen-oxygen compounds and sulfur dioxid may be continuously introduced at the beginning of the acid making apparatus, as will produce at the end of such apparatus a mixture'of the 1 different oxide of nitrogen in that propor sumption of nitrogen compounds.

tion which will be most completely absorbed in the apparatus for the absorption of oXids pounds have been introduced; (6) in ad justing the quantity of nitrogen compounds introduced at the beginning of the apparatus, to suit the requirements as indicated by the aforesaid sulfur dioxid determinations; and (0). in an improved method'for determining the percentage of sulfur dioxid in gas mixtures containing nitrogen-oxygen compounds.

In the following detailed description of my invention, reference is made for the sake of simplicity and clearness to only one type. of those processes using nitrogen-oxygen compounds in the manufacture of sulfuric acidnamel v, the chamber process. My

Specification of Letters Patent.

Patented Nov. 2i, rare.

' Application filed February 25, 1915. Serial No. 10,508.

claims, however, are not to be understood as restricted to the chamber process only, but on the contrary I here state explicitly that they are applicable to all processes in which any nitrogen-oxygen compound or compounds are used in the manufacture of sulfuric acid.

As is well known, the five prominent elements of a chamber plant are: 1. The burners, or furnaces, for generating sulfur dioxid. 2. The niter plant, in which raw nitrogenous material (usually NaNO is introduced. 3. The Glover tower, in which the chamber acid is concentrated, and the nitrous vitriol isdenitrated. 4. The chambersthe oxidizing, hydrating and condens other four parts of-the apparatus in the order named above. The percentage of su1- fur dioxid present in thegas (assuming no dilution by air or other gases) remains "constant from'the time of leaving the burners until the niter plant is reached (or Glover The sulfur-bearing gas, generated in the burners, or furnaces, passes w through the tower if there be no niter plant). Thereafter the percentage. of sulfur dioxid is gradually reduced, as the gasestraverse the several parts of the apparatus, owing to the constant oxidation of sulfur dioxid, induced by the nitrogen compounds. This oxidation of sulfur dioxid will proceed the more. rapoxygen compounds introduced at the niter plant and Glover tower, in proportion to the sulfur dioxid admitted. The converse of this is also true. The economical operation of the process demands that such a quantity of nitrogen-oxygen compounds be introduced at the niter plant and Glover tower as willinduce oxidation of the sulfur dioxid in the chambers at that rate of speed which is idly, the greater the quantity of nitrogen-- found by experience to yield -the most complete absorption of the oxids of nitrogen in the Gay-Lussac tower. If too much of the nitrogen-oxygen compounds be introduced at the niter plant and Glover tower, the oxidation of sulfur-dioxid will proceed so rapidly as to permit an excess of nitrogenv peroxid, above the desired proportion of the atmosphere. If, on the other hand, too

little of the nitrogen-oxygen compounds be introduced at the beginning of the apparatus, th oxidation of the sulfur dioxid will be so retarded that an excess of nitric oxid, above the desired proportion, will exist in the gases about to enter thev Gay-Lussac tower, resulting in inefficient operation and loss of values as before.

Prior to my invention, the means used to indicate to the acid plant operator the proportion of the oxids of nitrogen to sulfur dioxid in the chamber gases gave tardy information, or were unreliable and inexact. As examples of the best of such unreliable means I mention (a) inspection of the color of the chamber gases through glass windows or sights and (b) observance of the difference between the temperatures of the gases at certain fixed places in the chamber system. a

((I.)- Since on account of the white mlsts and fumes existing in the front chambers it is impossible there to detect slight variations in the color of the gases, it is customsults.

ary to view the color of the gases in an mtermediate chamber or inthe'last chamber, where variations in shade are more easily perceptible. Such information as is gained from noting the color changes in these chambers comes, however, too late to be of much,- practical use to the observer. Forv if anything is wrong with the proportions of the various gases in the chambers, the fact is not known until the chambers are full of the-troublesome gas mixture up to the point of observation of the color of the gases, and it is then impossible to apply the remedy in time to avoid losses in the Gay-Lussac tower.

Furthermore, observance of the differing colors of "the chamber gases gives information which is at best unreliable and inexact,

' tatively.

and incapable of being expressed quanti- (b) The observance of the difierences between chamber temperatures is liable to lead to erroneousv conclusions, and to the apphcation'of improper remedies, because changes in'the temperature differences may be due to a' number of different causes, such as changes in the composition of burner gas,

1 changes in the atmospheric temperature,

rain, or excessive or deficient supply of nit'rogen compounds. 'On this account the observance'a of temperature changes alone is anunsa fefguide in regulating the chamber process, and leads at times to serious losses. I This methodof controlling the chambers is moreover an inexact method.

Prior to my invention it was impossible to regulate the proportion of nitrogen oxids to sulfur dioxid inflthe chambers by means of chemical an'alysisof the chamber gases,

because, first, no reasonably accurateandquick method was known, prior to my invention; of determining the percentage of sulfur dioxid or of any other component of chamber gas, with a sufiicient degree of accuracy and with at the same time suflicient speed to be of practical use for the purpose; and secondly, because prior to my discovery it was not known that definite ratios could be established between the percentage of sulfur dioxid in the burner gas, and a corresponding percentage of sulfur dioxid desirable for any chosen point in the front end of a chamber plant. It was impossible, prior to my invention, to obtain accurate, definite, and immediateinformation regarding the composition of the gas mixture within the chambers, at the very beginning of the acid-condensing system. Consequently it was impossible to apply proper remedies for existing trouble in the composition of chamber gas immediately, intelligently, and with certaintyof securing the desired re- In short, prior to myinvention the proper proportion of oxids of nitrogen to sulfur dioxid in the chamber gases could not be accurately maintained by the means then known, and consequently the proportion of nitric oxid to nitrogen peroxid desirable in the G'ay-Lussac tower was not constant, and values were lost, which by my process are recoverable.

By the application of my invention, it is now possible to maintain the correct proortion ofoxids of nitrogen to sulfur dioxid 1n the chamber gases continuously, to correct immediately anythreatened excess of either nitrogen oxids or sulfur dioxid, and in this way to effect great economy in the operation of the chamber process. Whereas the old methods'of controlling the chamber process give tardy information, in time of trouble, that something is wrong, my method gives lmmediate information a's'to precisely what is wrong, and to what extent;

The method which I have invented for the indication of the proportion of nitrogen V the niter plant and Glover tower, consists in the determination of the percentage of sulfur dioxid in the chamber gases at any point or points in the chamber system where the percentage of sulfur dioxid should be normally more than seven-tenths of one per cent. by volume (but preferably at a point in the first half of the chamber space near enough to the Glover tower to be reached by the gases within twenty minutes or less after leaving that tower) and in the intelligent comparison of such determinations with sulfur dioxid determinations made on the gas at some other point or points in the acid plant.

I have discovered that, at any given point in the chambers or chamber gas connections centage of sulfur dioxid in the burner or furnace gases which are free from nitrogen compounds, for any one grade of burner gas, provided the oxids of nitrogen and thesulfur dioxid in the chambers are maintained in the proportion required to produce the most complete recovery of nitrogen oxids in the Gay-Lussac tower. I have found further that any excess of oxids of nitrogen will be definitely indicated, by a decrease in the sulfur dioxid-ratio, below what is desirable; and, conversely that any deficiency of oxids of nitrogen will be definitely indicated by an increase in the sulfur dioxid ratio, above what is desirable; such decrease or increase in the said ratio being an accurate measure of the extent of the excess or deficiency of nitrogen oxids, I have found that, by adjusting the quantity of nitrogen,

compounds, or of sulfur dioxid (or of both) admitted to the chambers, in such a way as to meet the requirements as indicated by the sulfur dioxid determinations on chamber gas, at pre-determined points in the system, it is possible to maintain the desired proportion of nitrogen oxids to sulfur dioxid indefinitely, resulting iii a markedincrease in the quantity of nitrogen oxids recovered in the Gay-Lussac tower, and hence in much greater economy of operation of'the chamber process.

To secure definite and valuable' results, it

' is only necessary to select a suitable point in the chamber system,-to determine once for all by repeated sulfur dioxid determinations, whatis the desirable ratio between the percentage of sulfur dioxid at the point se- 'lected and the. percentage of sulfur dioxid in the burner or furnace gas, for each of the various grades of burner gas (meaning by .grade. of gas its percentage of sulfur di oxid) and thereafter to so adjust the quantities of nitrogen compounds and sulfur diconditions)- between five one-hundredth-s (.'O5 and fifteen one-hundredths (.15) of -one'per cent. by volume, the lower percentages say .05 to .11 per cent. being desirable in cold weather, and the higher percentages, say .09 to .15 per cent. being desirable in warm weather I have found, moreover,

that while the desirable percentage of sulfur.

dioxid in the chamber gas, at any chosen point in or near the Glover tower, will fluctuate with fiuctuations 1n the grade of the burner gas, the desirable sulfur dioxid percentage in the gases about to enter the Gay-Lus sac tower is, within the limits specified, a fixed quantity, regardless of fluctuations in the grade of the burner gas. I have found that the percentage of sulfur dioxid in the gases about to enter the Gay-Lussac tower can be maintained indefinitely within the desirable limits above stated by establishing and maintaining the desirable ratios between the percentage of sulfur dioxid in thegases at any chosen point in the Glover tower, or front chambers, and the percentage possible rade ofburner gas. I have found that sul ur dioxid tests made on the gases comparatively near the end of the system, for example those about'to enter the Gay- Lussac tower, in combination with sulfur dioxid determinations made at a point or points in the chamber system nearer to the of sulfur dioxid in the burner gas, for each Glover tower (or even inside that tower) are a useful guide in determining the desirable to the Glover tower (or even in that tower 1 itself) are a useful guide in checking the accuracy'of the operator making the latter determinations; and that therefore such a combination of tests for sulfur dioxid is a useful and valuable one in controlling the,

acid making process, although with reliable tests at the front of the chamber system, the sulfur dioxid'tests at the back of the system are notessential to economical operation. I

At the time of making my early'eXperiments with the determination of sulfur dioxid in chamber gas, I found that the known methods for such determinations were not at once sufficiently rapid and ac:

curate to secure the results. desired. The most rapid and convenient method was that known as Reichsv method,the method in common use for the determination of sulfur 'dioxid in burner gas. According to this method, the gas under examination is aspirated through water containing a measured quantlty of standard iodin solution,

colored blue by starch solution, and contained in an absorption bottle provided with two glass tubes, one long and one short; the long one being connected by rubber tubing'to the chamberor flue containing the gas to be treated, and the short one to the top of a large bottle containingv water, and fitted as an aspirator by havin an outlet'for the water near the bottom, with rubber tube and this happens the stopcock regulating the flow of water from the aspirating bottle is instantly closed. The volume of water collected in the measuringcylinder is a measure of the volume of gas aspirated through the iodin solution, and so of the percentage of sulfur dioxid in the gas. By reference to published tables the volume of water collected may be readily interpreted into the percentage of sulfur dioxid. This method is 'sufiiciently accurate for burner gas, but when applied togases containing oxids of nitrogen, it is found that these oxids tend to decompose the hydriodic acid as formed in the absorption bottle, liberating free iodin again. It is obvious that ifthe known quantity of'iodin which is introduced into the absorption bottle for the purpose of making an accurate assay be increased by an un-v known quantity liberated by the oxids of nitrogen from the hydriodic acid formed in the early stages of an assay or in a previous assay, the results are vitiated. This liberation of free iodin from the products of a preceding assay, or of the early stages of an assay, is attested by the prompt recurrence of the starch-iodin blue color immediately after that color has been discharged, when operating on gases containing oxids of nitrogen. The inference is that this liberation of free iodin is progressing all the time that the gas is being aspirated; hence that at least more iodin is acted upon by the gas than the measured quantity introduced for the assay; hence that more gasis drawn through the absorption bottle than would have been necessary to decolorize exactly the amount of iodin introduced for the assay hence that the indicated result, in percentage of sulfur dioxid, is too low. Furthermore, duplicate tests made on the same gas in rapid succession will not, if oxids of nitrotempting to make an estimation of sulfur dioxid by the ordinary Reich test, sooner or later to discharge the blue color of the solution; but the indicated results will invariably be too low, and corroborative results can- .not be obtained. The end point is uncertain, and often the operator, when under the impression, from the increasing paleness of the solution, that the'color is about to be completely discharged, finds that the blue color suddenly becomes more intense, instead of continuing to fade. In the last chamber, where the percentage of sulfur dioxid approaches the minimum, it is often entirely impossible to decolorize the solution at all, so; quick'and effective is the action of the oxids of nitrogen in restorin the iodin in uncombined form to the solution, due to the larger ratio of the higher oxids of nitrogen to sulfur dioxid therein.

It is therefore plain that the ordinary Reich test fails to give accurate and reliable indication of the S0 content when applied to gases containing the oxids of nitrogen present in chamber gas, and in the last chamber of a sulfuric acid plant often fails to give any indicationwhatever. However, the Reich test, as applied to gases free from oxids of nitrogen, is so convenient, rapid,

and accurate, that it seemed the most desirable method possible for testing chamber gas, if onlyv some means could be found to prevent the interfering action of the oxids of nitrogen, without impairing the reliability of the test. I have succeeded infinding such ameans.

I have invented an improvement in Reichs method for sulfur dioxid determinations, by the adoption of which the recurrence of the blue color may. be either prevented altogether, or may be so delayed as not to interfere with the accuracy of a test, to any perceptible degree. My improvement consists in the addition to the absorption bottle or absorption liquid, of a Reichs or other sulfur dioxid determinathe carbonate, sulfate, acetate, or other salt of potassium, sodium,'zinc, or other base (but preferably the acetate of sodium) together with a suiiioient amount of acid (for example, sulfuric, acetic, or hydrochloric acid or an acid anh'ydrid, said acid being without oxidizing or reducing. action on hydriodic acid or iodin): to render the solution acid.

Without limiting myself to the exact materials or amounts given, I give the'following example of the solution to be used in the absorption bottle: N/lO iodin solution, 1 c. c.; water, 100 c. c.; starch solution, 5-6- drops, and sodium acetate mixture, 10 c. c. This sodium acetate mixture may be prepared by adding one volume of acetic acid (say 95%) to five volumes of saturated sodium acetate solution,

I do not limit myself to the particular inafter described is obvious.

dioxid it is possible at any time to make sulfur dioxid determinations in duplicate on gas mixtures containing oxids of nitrogen which will check each other within one one-hundredth (.01) of one per cent.a degree of accuracy which is not attained by any other method for the analysis of such gas mixtures, so far as I am aware. Since my improved method requires no longer time for its execution than the ordinary Reich test, its value for the purposes here- I have discovered that my improved method for making sulfur dioxid determinations can be most usefully applied to my hereinbefore described method of controlling the proportions of nitrogen oxids and of sulfur dioxid, by means of sulfur dioxid determinations on the chamber gases made at a' point comparatively near the Glover tower, either at that one point alone, or in combination with similar tests made 'on gases containing nitrogen oxids at a point or points nearer to the Gay-Lussac tower, 01' even inside that tower.

Although I have invented the above described improvement in the method of making determinations of the percentage of sulfur dioxid in gas mixtures containing oxids of nitrogen, which improvement I have discovered to be useful in connection with my improved method for the control of processes for the manufacture of sulfuric acid, I desire to state explicitly that my improved method of controlling processes for the manufacture of sulfuric acid, described above, is not necessarily limited to the use of my own improved method for sulfur dioxid determinations. On the contrary it is to be clearly understood, that my invention for the control of sulfuric acid processes comprises the use of sulfur dioxid determinations made at any part of the chamber system where the percentage of sulfur dioxid, in gas mixtures containing oxids of nitrogen is normally more than seventenths (.7) of one per cent. by volume (in whatever way such determinations may be made.

' and regardless of whether such determinations be made at one point only, or at more than one point in the chamber system, or in combination with similar tests made on the gases comparatively near the end of the chamber system, or about to enter or in the bottom of the Gay-Lussac tower) for the purpose of controlling the proportions of nitrogen compounds and sulfur dioxid (or either of these) admitted to the chambers.

While I have mentioned, in my description of the secondary or checking test on gases containing oxids of nitrogen, that this is applicable to the gases about to enter the Gay-Lussac tower, which would normally contain .05 to .15 per cent. sulfur dioxid, I will state that this test can if desired be made at other points in the latter part,say, at least the latter third of the chamber space. Thus this secondary or checking test might be made on gases which woul not reach the Gay-Lussac tower for as much as fifteen or twenty minutes, or perhaps even longer; and the normal percentage of sulfur dioxid in the gases chosen for the secondary test might be as high as .65 per cent. or in some cases even higher. Any point in the latter part of the chamber system where the desirable percentage of sulfur dioxid remains substantially constant, regardless of fluctuations in the percentage of sulfur dioxid in the burner gas, may be chosen for the secondary or"checking test,

or for tests to be used in establishing desirable sulfur dioxid ratios.

The' method of determining sulfur dioxid in gas mixtures such as those referred to in the present application, namely mixtures containing sulfur dioxid and also containing oxids of nitrogen, are not claimed in thepresent application, but form the sub ject matter of my copending application Ser. No. 80,037 filed February 23, 1916.

What I claim is 1. In the manufacture of sulfuric acid the step of regulating the relative amounts of nitrogen-oxygen compounds and sulfur dioxid introduced, in such a manner as to maintain at a predetermined given place in the acid-making system, a predetermined substantially uniform percentage of sulfur dioxid in the gases, said percentage being more than 0.7% by volume. V

.2. In the manufacture of sulfuric acid, the improvement which consists in determining that ratio between the percentages of sulfur dioxid in the gases at two predetermined places in the acid-making system, best adapted to a commercially complete absorption of nitrogen-oxygen compounds, at least one of said places being located in that part of the system where the normal percentage of SO should be over 0.7 and thereafter maintaining said ratio, by regulation of the relative amounts of nitrogenoxygen compounds and sulfur dioxid introduced into the system.

3. In the manufacture of sulfuric acid, the improvement which comprises determining. by means of analyses of the gases at a plurality of separated points of the acid making plant, the proper ratio between the percentage of sulfur dioxi'd in the gases free from nitrogen-oxygen compounds entering the acid making system, and the percentage of sulfur dioxid in the gases containing nitrogen-oxygen compounds at a predetermined point in the acid making system where the percentage should normally ,be more than 0.7% by volume, and maintaining the proper ratio substantially constant, by regulating the relativeamounts of nitrogen-oxygen compounds and sulfur tem.

4. In the manufacture of sulfuric acid, 3 the improvement which comprises determining the proper ratio between the percentages of sulfur dioxid in the gases free from nitro e'n-oxygen compounds entering theacidma ring system, and the percentage of sulfur dioxid in the gases containing nitrogenoxygen compounds at a predetermined point in or near the Glover tower, by means of analyses of said gases, and maintaming said ratlo substantially constant by regulating the relative amounts of nitrogen-oxygen.

compounds and sulfur dioxid introduced.

. 5. In the manufacture of sulfuric acid the step of determining the proper ratio for sulfur dioxid containing gases of different grades, between the percentages of sulfur dioxidin the gases free from nitrogenoxygen compounds entering the acid making system and the percentages ofsulfur dioxid in the gases containing nitrogen oxygen; compounds, at a predetermined place in the acidmaking system where the percentage of sulfur dioxid shouldnormally he more than 0.7 70 by. volume, and thereafter regulating the amounts of oxygen-nitrogen compounds introduced, in accordancewith the amount and grade of said incoming. gases, in such a manner as to maintain the above mentioned proper ratio corresponding to .the

particular grade of gas being employed.

6'. The herein. described method .of Controlling the; manufacture of sulfuric acid," which method comprises determining the" desirable ratio between the percentage zof a sulfur dioxid at any given POlIlt lIl a sul-l furic acid plant, where the gas mixturenor; mally contains nitrogen-oxygen compounds,

: and the percentage ofsulfur dioxid in the incoming gases free from nitrogen-oxygen co-mpounds, and in so regulating the rela tive amounts of nitrogen-oxygen compounds and of sulfur dioxid supplied to the apparatus, as to substantially maintain such ratio, substantially as described.

7. In the manufacture of sulfuric vacid, the improvement which comprises determining the proper ratio between the percentages of sulfur dioxid in the gases at two predet0 termined points in the acid making apparadioxidintroduced into the acid making-systaining nitrogenoxygen compounds at a predetermined point comparatively near the front end of theacid making system, and

determining the amount of sulfur dioxid in the gases at a predetermined point comparatively near the Gay-Lussac tower or towers,

and so regulating the operation of the chambers as toxmaintain a predetermined percenso tage ofsulfur dioxid in the gases'at said last mentioned. point. Y 9. The improvement in the art of making sulfuric acid which comprises making sul-- fur dioxid'determinations on gas mixtures containing oxids of nitrogen at any point in a sulfuric acid plant Where the percentage of sulfur dioxid'lwould normally be more than 0.7 70, thereby determining theratio between the percentages of sulfur dioxid in the gases at different parts of a plant, and

proportioning the relative amounts of ni trogen compounds to sulfur dioxid in the gasesl supplied to theacid making apparatus,:so as to maintainsaid ratio substantiallyuniform. j, Y I 10. The hereindescribed-improvement in the sulfuric acid manufacture, said improvement' comprising the jfsteps of determining at frequentintervals, the percentage of sni .fur, dioxid (a) 'in the gases ata predeter 'mined pointin the acid making system-and near thefront endthere'of, and (b) .in" the burner gases which contain no 'oxids of 'ni' 'trogenand v(chin the gases at a p redeten mined point n rit rear end Ofthe sysg tem; and regulating the proportions of sulfur dioxid and of nitrogenoxygen compounds admitted. to the chambers so as to maintain that ratio between the percentages 11 0 of sulfur dioxid at the points (a) and (l)) which will produce and. maintain a desirable predeterminedpercentage of sulfur dioxid in the gases at the point (0).

Intestimony whereof I aflix my signature in presence'of two witnesses.

ANDREW MILLER FAIRLIE.

Witnesses 2-;

MINNIE HARMON, W. A. CHANABERRK. 

